1. Field of the Invention
The present invention relates to a cylindrical part manufactured by fiber reinforced plastic composite material so as to be used as a structural member, and a method of manufacturing the same cylindrical part by fiber reinforced plastic composite material.
2. Description of the Related Art
The fiber reinforced plastic composite material is excellent in specific strength, specific rigidity and corrosion resistance. However, there still exist various technical problems to be solved when a structural member is manufactured by fiber reinforced plastic composite material.
When a thick-walled cylindrical part is manufactured by the fiber reinforced plastic composite material, various methods such as filament winding method, tape winding method, sheet winding method, and etc. are now being adopted.
However, the fiber reinforced plastic composite material is provided with such characteristics that a thermal expansion coefficient thereof differs largely according to the lamination direction. Therefore, when a thick-walled cylindrical part is manufactured by the fiber reinforced plastic composite material, internal stress proportional to a difference between curing temperature and room temperature is inevitably generated in the fiber reinforced plastic composite material, after heated for curing. In the case of the thick-walled cylindrical part, there exists the case where the internal stress generated in the fiber reinforced plastic composite material exceeds an interlayer bonding strength of the fiber reinforced plastic composite material. In this case, an interlayer separation occurs in the fiber reinforced plastic composite material.
In a general laminating process of thick-walled cylindrical parts, many lamination angles of xc2x110xc2x0/xc2x145xc2x0/xc2x185xc2x0 are combined with each other. In this case, when a diameter of the cylindrical part is small (e.g., less than 200 mm) and the wall thickness is large (e.g., more than 30 mm), since the internal stress becomes excessively large, there exists a problem in that the interlayer separation occurs.
To overcome this problem related to the interlayer separation, Japanese Published Unexamined (Kokai) Patent Application No. 2-236014 discloses such a method of laminating a layer strengthened against torsion (of which the lamination angle is xc2x130xc2x0 to xc2x160xc2x0 with respect to the axial direction) and the layer strengthened against bending (of which the lamination angle is 0xc2x0 to 20xc2x0) alternately, in order to suppress the interlayer separation due to a difference in the thermal expansion coefficient between the conditions when heated for curing and when cooled to the room temperature.
Further, Japanese Published Unexamined (Kokai) Patent Application No. 6-335973 discloses a method of using high frequency induction heating means, to reduce the temperature dispersion while heating for curing and thereby to decrease the internal stress thereof.
In the first prior art method of laminating plies at different lamination angles (i.e. directions), since the wall thickness of the manufacturable cylindrical parts is limited to about 15 mm, when the wall thickness thereof increases more than this value (e.g., 15 to 50 mm), the internal stress generated in the fiber reinforced plastic composite material sharply increases with increasing wall thickness, so that the interlayer separation occurs in the fiber reinforced plastic composite material layers. Therefore, it is impossible to manufacture a cylindrical structure of high strength and high rigidity by making the best use of the characteristics of the composite material.
Further, in the second prior art method of using a high frequency induction heating apparatus in order to reduce the temperature dispersion during the heat curing and thereby to reduce the internal stress generated in the fiber reinforced plastic composite material layers, since magnetic substances are added to the matrix resin, the weight thereof inevitably increases, as the result that there exists a problem in that the weight of the structural body is increased and further the performance of the structural body is degraded. In this method, additionally there exists another problem in that a special high frequency induction heating facility must be prepared in accordance with the shape of the manufactured structural body, instead of an autoclave or a heating furnace.
Further, when a mandrel formed of steel (thermal expansion coefficient: 10 to 12xc3x9710xe2x88x926/xc2x0 C.) is used, since the mandrel is shrank when cooled after heat curing, there exists a problem in that the inside layers are shrunk in the radial direction thereof and thereby the interlayer separation often occurs.
With these problems in mind, therefore, it is an object of the present invention to provide a method of manufacturing a thick-walled (e.g., 40 mm) cylindrical part having a stable quality by use of fiber reinforced plastic composite material, by reducing the internal stress thereof, while using the conventional equipment.
To achieve the above-mentioned object, the present invention provides a method of manufacturing the cylindrical part by fiber reinforced plastic composite material, which includes the step of laminating a fiber reinforced plastic composite material with an elastic modulus on a mandrel, winding a different kind of said composite material with another elastic modulus on said fiber reinforced plastic composite material, repeating alternately said laminating and said winding, curing both of said materials, and deriving a fiber reinforced plastic product without deformation due to internal stress after cooling down and taking out said mandrel.
Further, the present invention provides a method of manufacturing the cylindrical part by the fiber reinforced plastic composite material, comprising the steps of: laminating a fiber reinforced plastic composite material having a small thermal expansion coefficient in a circumferential direction of a metallic mandrel; heating the laminated fiber reinforced plastic composite material for curing, to form an auxiliary member; laminating another fiber reinforced plastic composite material on an outer side of the formed auxiliary member; and heating the formed laminated fiber reinforced plastic composite material for curing.
Further, the present invention provides a method of manufacturing a thick-walled cylindrical parts by fiber reinforced plastic composite material, comprising the steps of: laminating a fiber reinforced plastic composite material having a small thermal expansion coefficient in a circumferential direction of a mandrel; heat-curing the laminated composite material under first heating conditions to form an auxiliary member; covering the formed auxiliary member with a thin film of high heat resistance; laminating another fiber reinforced plastic composite material on the thin film covering the auxiliary member, to form a first fiber reinforced plastic composite material layer; laminating another fiber reinforced plastic composite material having an elastic modulus smaller than that of the fiber reinforced plastic composite material of the first fiber reinforced plastic composite material layer, on the formed first fiber reinforced plastic composite material layer, to form a second fiber reinforced plastic composite material layer; laminating another fiber reinforced plastic composite material the same as that of the first fiber reinforced plastic composite material layer, on the formed second fiber reinforced plastic composite material layer, to form a third fiber reinforced plastic composite material layer; laminating another fiber reinforced plastic composite material the same as that of the second fiber reinforced plastic composite material layer and another fiber reinforced plastic composite material the same as that of the third fiber reinforced plastic composite material layer, alternately by a predetermined times, on the formed third fiber reinforced plastic composite material layer; compaction-processing all the laminated fiber reinforced plastic composite material layers under second heating conditions at a temperature lower than and for a time shorter than those of the first heating conditions, to form a strength member; laminating another fiber reinforced plastic composite material the same as that of the second fiber reinforced plastic composite material layer and another fiber reinforced plastic composite material the same as that of the third fiber reinforced plastic composite material layer, alternately by a predetermined times, on the formed strength member; compaction-processing all the laminated fiber reinforced plastic composite material layers under the second heating conditions, to form another strength member; laminating another fiber reinforced plastic composite material the same as that of the second fiber reinforced plastic composite material layer and another fiber reinforced plastic composite material the same as that of the third fiber reinforced plastic composite material layer, alternately by a predetermined times, on the formed strength member, to form a thick-walled cylindrical body having a predetermined thickness on the formed strength member; and heat-curing all the laminated fiber reinforced plastic composite material layers under the first heating conditions.
Further, the present invention provides a thick-walled cylindrical part manufactured by the fiber reinforced plastic composite material includes a plurality of sorts of fiber reinforced plastic composite materials which have a different elastic modulus and alternately laminated respectively.
In the method of manufacturing the thick-walled cylindrical part by composite material according to the present invention, in order to reduce the internal stress generated in the fiber reinforced plastic composite material layer after heat curing, when the major material of the thick-walled cylindrical part is a carbon fiber reinforced plastic composite material, a cushioning material (e.g., glass or aramide fiber reinforced plastic composite material) having an elastic modulus smaller than that of the carbon fiber reinforced composite material is laminated separately about several to 20% being divided into several layers in the wall thickness direction. By these lamination layers, it is possible to reduce the internal stress generated in each layer and thereby to eliminate the interlayer separation caused after heat curing of the cylindrical part.
Further, during the lay-up processing, the laminated cylindrical part is processed for a compaction method at temperature (e.g., 60xc2x0 C. to 130xc2x0 C.) lower than the curing temperature (e.g., 180xc2x0 C.) for a time (e.g., 30 to 60 min.) and under pressure (e.g., vacuum to 7 kgf/cm2); that is, under such conditions that no harmful influence is exerted upon the physical properties of the finally cured cylindrical part. By this compaction process, it is possible to reduce a change in the wall thickness thereof between the conditions when laid-up and after heated and to prevent the occurrence of local meandering and local wrinkles produced after heated for curing; that is, to decrease the internal stress.
Further, since the auxiliary member formed by the fiber reinforced plastic composite material layer having a small thermal expansion coefficient in the fiber direction is laminated inside the strength member required to increase the strength and the rigidity, it is possible to prevent the inner layers from being shrank after the strength member is once heated for curing and then cooled, so that the interlayer separation of the thick-walled cylindrical part can be prevented. Here, as the composite material used for this purpose, the carbon fiber reinforced plastic composite material having a roughly zero thermal expansion coefficient in the fiber direction is suitably used.
Further, since the occurrence of the internal stress is proportional to the difference between the curing temperature and the room temperature, it is possible to reduce the temperature difference between the conditions when heated for curing and when cooled by reducing the curing temperature within such a range that the performance is not degraded as compared with the case obtained in the conventional curing cycle. As a result, it is possible to reduce the internal stress after the heat curing.
Further, according to the wall thickness and the usage, it is possible to suppress the occurrence of the internal stress by changing the lamination direction of the fiber reinforced plastic composite material.